Early humans (before Homo sapiens)

Early members of the Homo
genus, i.e. Homo ergaster,
Homo erectus and Homo heidelbergensis migrated from
Africa during the Early
Pleistocene, possibly as a result of the operation of the
Saharan pump, around 1.9 million
years ago, and dispersed throughout most of the Old World, reaching as far as Southeast Asia. The date of original
dispersal beyond Africa virtually coincides with the appearance of
Homo ergaster in the fossil record, and the associated
first emergence of full bipedalism, and
about half a million years after the appearance of the
Homo genus itself and the first stone tools of the Oldowan
industry.Key sites for this early migration out of
Africa are Riwat in Pakistan
(1.9 Mya), Ubeidiya in the
Levant (1.5 Mya) and Dmanisi in the
Caucasus (1.7 Mya).

China was populated more than a
million years ago,as early as 1.66 Mya based on stone artifacts
found in the Nihewan Basin.Stone tools
found at Xiaochangliang site were
dated to 1.36 million years ago.The archaeological site of Xihoudu ( ) in Shanxi Province is
the earliest recorded use of fire by Homo erectus, which is dated
1.27 million years ago.

The broad study of African genetic diversity headed by Dr.Sarah
Tishkoff found the San people to express the
greatest genetic diversity among the 113 distinct populations
sampled, making them one of 14 "ancestral population clusters."
The
research also located the origin of modern human migration in
south-western Africa, near the coastal border of Namibia and Angola.

Around 100,000-80,000 years ago, three main lines of Homo
sapiens diverged. Bearers of mitochondrial haplogroup L1 (mtDNA) / A (Y-DNA) colonized Southern Africa
(the ancestors of the Khoisan (Capoid) peoples), bearers of haplogroup L2 (mtDNA) / B (Y-DNA) settled Central and West
Africa (the ancestors of Niger-Congo and
Nilo-Saharan speaking peoples and of
the Mbuti pygmies), and bearers of haplogroup
L3 remained in East
Africa.

Exodus from Africa

According
to the Recent
African Origin hypothesis a small group of the L3 bearers
living in East Africa migrated north
east, possibly searching for food or escaping climate changes,
crossing the Red
Sea about 70 millennia ago, and in the process going on
to populate the rest of the world.

Around 50,000 years ago the world was entering the last ice age and
water was trapped in the polar ice caps, so sea levels were much
lower. Today at the Gate of Grief the Red Sea is about 12 miles (20 kilometres) wide
but 50,000 years ago it was much narrower and sea levels were 70
metres lower. Though the straits were never completely
closed, there may have been islands in between which could be
reached by simple rafts. Shell middens 125,000
years old indicate that the diet of early humans in Eritrea included sea
food obtained by beachcombing.
This has been seen as evidence that humans may have crossed the Red
Sea in search of food sources on new beaches.

South Asia and Australia

Some genetic evidence points to migrations out of Africa along two
routes. However, other studies suggest that a single migration
occurred, followed by rapid northern migration of a subset of the
group. Once in West Asia, the people who
remained south (or took the southern route) spread generation by
generation around the coast of Arabia and
Persia until they reached India. One of the groups that went
north (east Asians were the second group) ventured inland and
radiated to Europe, eventually displacing the Neanderthals. They
also radiated to India from Central Asia. The former group headed
along the southeast coast of Asia, reaching Australia between
55,000 and 30,000 years ago, with most estimates placing it about
46,000 to 41,000 years ago.

During that time, sea level was much lower and most of Maritime Southeast Asia was one land
mass known as the lost continent of Sunda. The settlers probably continued on the
coastal route southeast
until they reached the series of straits
between Sunda and Sahul, the
continental land mass that was made up of present-day Australia and
New
Guinea. The widest gaps are on the Weber Line and are at least 90 km wide,
indicating that settlers had knowledge of seafaring skills. Archaic
humans such as Homo erectus never reached Australia.

If these dates are correct, Australia was populated up to 10,000
years before Europe. This is possible because humans avoided the
colder regions of the North favoring the warmer tropical regions to
which they were adapted given their African homeland. Another piece
of evidence favoring human occupation in Australia is that about
46,000 years ago, all large mammals weighing more than 100 kg
suddenly became extinct. The new settlers were likely to be
responsible for this extinction. Many of the animals may have been
accustomed to living without predators and become docile and
vulnerable to attack (as occurred later in the Americas).

While
some settlers crossed into Australia, others may have continued
eastwards along the coast of Sunda eventually turning northeast to
China and finally reaching Japan, leaving a
trail of coastal settlements. This coastal migration leaves
its trail in the mitochondrial haplogroups
descended from haplogroup M,
and in Y-chromosomehaplogroup C. Thereafter, it may have
become necessary to venture inland possibly bringing modern humans
into contact with archaic humans such as H. erectus.
Recent genetic studies suggest that Australia and New Guinea were
populated by one single migration from Asia as opposed to several
waves. The land bridge connecting New Guinea and Australia became
submerged approximately 8,000 years ago, thus isolating the
populations of the two land masses.

Europe

Europe is thought to have been colonized by northwest bound
migrants from Central Asia and the Middle East. The expansion is
thought to have begun 45,000 years ago and may have taken up to
15,000 years for Europe to be fully colonized. During this time the
Neanderthals were slowly being displaced. Because it took so long
for Europe to be overrun, it appears that humans and Neanderthals
may have been constantly competing for territory. The Neanderthals
were larger and had a more robust or heavy built frame which may
suggest that they were physically stronger than modern Homo
sapiens. Having lived in Europe for 200,000 years they would
have been better adapted to the cold weather. The anatomically
modern humans known as the Cro-Magnons,
however, with superior technology and language would eventually
completely displace the Neanderthals, whose last refuge was in the
Iberian
peninsula. After about 30,000 years ago the fossil
record of the Neanderthals ends, indicating that they had become
extinct. The last known population lived around a
cave system on the remote south-facing coast of Gibraltar from 30,000 to 24,000 years ago.

Proponents of the multiregional
hypothesis have long believed that Europeans were descended
from Neanderthals (which also came from
Africa, evolving in Europe from Homo Ergaster), and not from this homo-sapiens
migration. Others believed the Neanderthals had interbred with
modern humans. In 1997 researchers managed to extract mitochondrial
DNA from a 40,000 year old specimen of a Neanderthal. On comparison
with human DNA, its sequences differed significantly, indicating
that based on the mitochondrial DNA, modern Europeans are not
descended from the Neanderthals and that no interbreeding took
place. Some scientists continue to search autosomal DNA for traces
of Neanderthal admixture. A few alleles of some autosomal genes
such as the H2 allele of the MAPT gene have been suggested, since
they were only found among Europeans. However in the absence of
autosomal DNA from a Neanderthal, the scientists conclude that this
hypothesis is entirely speculative.

Some archaeologists doubt that Neanderthals and Homo
sapiens were interfertile. This is because Neanderthals and
Europeans shared the same habitat for up to 20,000 years, yet no
undisputed skeletal fossils have been found that show intermediate
properties between the two species.

Central and Northern Asia

Mitochondrial haplogroups A, B and G originated about 50,000 years ago,
and bearers subsequently colonized Siberia, Korea and
Japan, by about 35,000 years
ago. Parts of these populations migrated to North
America.

The Americas

The
Americas were occupied by people who crossed from Siberia into Alaska. At
the time sea levels were lower and a land bridge of the lost
continent of Beringia connected North
America to Eurasia. It is likely they used
the southern route that may have been much warmer.

There is considerable controversy over when the Americas were first colonized and how many
migrations there were. Controversial findings in Chile at Monte Verde may indicate a human presence in the Americas by up
to 33,000 years ago. The oldest indisputable evidence of
human presence in the Americas are, however, findings related to
the Clovis culture, which have been
dated to about 11,000 years ago. The findings of Clovis points indicate the early settlers
hunted large animals. About the same time as the arrival of the
clovis culture many large animals such as Mammoths became extinct (as in Australia, possibly
due to hunting).

Linguist Joseph Greenberg
controversially classified American languages into three major
families: Eskimo-Aleut,
spoken by the Inuit peoples; Na-Dené, comprising 32 languages
spoken only in North America by the Apache,
Navajo, and tribes in Alaska and Canada; and Amerind, comprising more than 500
languages spoken in North and South America. Greenberg suggested
that these three languages families represented three separate
migrations that filled the Americas in the order they
arrived.